Integrated circuits are manufactured from semiconductor wafers that are conventionally round in shape and made of highly brittle silicon. Such wafers are subjected to a variety of processing steps in transforming the semiconductor wafer into integrated circuit components. The various processing steps must be performed under ultra-clean conditions to minimize the potential of contamination of the wafers as they are being processed. Each wafer may be subjected to dozens, if not hundreds of steps in its processing cycle. The potential for contamination and destruction of a wafer or reduction in yield is ever-present throughout the various processing and packaging steps. Particularly during the steps that take place at fabrication facilities, any minute particulates can destroy the integrated circuit on which it falls. Once the processing steps of the wafers are completed, they are generally shipped while still in wafer form to a facility that will dice and encapsulate, in integrated circuit packaging, each individual circuit on the wafer.
The stringent particulate control that takes place during the processing steps is generally not necessary in shipping the completed wafers to the facility that dices and packages the individual circuits.
Traditionally, during the processing, storage and shipping of semiconductor wafers, the wafers are supported and constrained at their edges to prevent any contact, possible damage and contamination to the faces of the wafers having the circuits thereon.
Even as semiconductor wafers are getting larger in scale, now up to 300 millimeters in diameter, the density of components is getting significantly greater. Moreover, disks are also are getting thinner, providing much thinner completed integrated circuit packages. This has been driven, at least in part, by the cellular phone industry that has sought thinner cell phones.
Accompanying the trend towards larger, more dense and thinner wafers, the wafers are becoming more valuable, more brittle and more easily damaged during shipment. Although it is possible, desirable, and common to ship thicker wafers in enclosed containers that would support the wafers exclusively by their edges, using such devices to ship the thinner wafers has proven problematic due to breakage and damage of the wafers.
Thus, for the thinner more fragile wafers, enclosures are utilized which have the wafers axially stacked on top of one another and separated by layers of paper-like flexible sheet material. Thus, the support of each wafer is by adjacent wafers and the entire stack of wafers. Foam material, such as urethane, is used to cushion the top and bottom of the stack.
Such shippers can also be configured to receive film frames. The film frames are packaged similar to the wafers and protected during transport.
One type of prior art wafer carrier is disclosed in U.S. Pat. No. 5,553,711 to Lin. Lin discloses a container that has a base, upright sidewalls defining a circular pocket, wafer dividers and a cover that comes down and threadingly attaches to the base.
FIG. 1 discloses a conventional wafer carrier in which the enclosure is defined by a cookie tin-like plastic container having a bottom 50, a top lid 52, and utilizing a circular urethane foam bottom cushion 54, and sheet material 56 interspersed between the wafer 58.
Referring to FIGS. 2 and 3, another wafer shipper is disclosed for shipping the stacked wafers with dividers therebetween. This wafer shipper has a base 60 and a top cover 62. The base and top cover are injection molded and have circular shaped and axially-extending structural members 64 in the base component. Similarly, the top cover has axially-extending circular structural members 64 and radially extending ribs 66 that also project axially.
These stacking wafer shippers may be either manually handled, robotically handled or both. Thus, means for opening and closing such containers must be both manually and robotically operable, and for manual purposes should be intuitive as well as simple, and reliable and quick. Various means are known for latching such wafer shippers. These include threads, such as shown in prior art FIG. 1, or a snap-on seal as shown in prior art FIGS. 2–3. Other means for latching are a minimal rotation thread as shown in the embodiment of prior art FIG. 4, and axially-projecting spring latches as discussed hereinbelow.
Wafer shippers that use the threaded engagements are awkward and subject to misalignment and improper attachment. These wafer shippers visually appear symmetrical in at least two planes, and therefore, there are typically four different options in assembling a top cover to a bottom cover. However, conventional prior art shippers generally require that the top cover be assembled in a specific orientation for proper latching.
U.S. Pat. No. 6,193,068 to Lewis, et al., discloses another type of conventional shipper featuring axially-extending spring latches and utilizing a double wall to define the pocket for the stack of wafer carriers. Said double wall thickness is defined by two spaced thin wall sections which are not attached to one another extending from the base. This configuration appears to allow the individual unsupported thin walls supported only at the base to take on and retain deformation. The concentric arrangement of the thin walls makes any such deformation visibly apparent. The double sidewall in this prior art embodiment may help to isolate direct impact on the top cover from direct communication from top cover structure to the wall defining the wafer pocket.
In the minimal rotation latch embodiment shown in FIG. 4, any separation stress will occur as illustrated by gap G. Such loading of the wafer shipper also can cause the deformation of the otherwise planar corners of the base to be stressed out of position, causing wobbling when placed on a planar surface and error in seating when placed on a machine interface. Such deformation can be caused in part by an overloading condition and also in part by the structural configuration of the wafer shipper.
It would be desirable to provide sufficient structure in the base of such wafer shipper to prevent such distortion and bowing. Moreover, it would be highly desirable to provide a wafer carrier that has indicating means therein to prevent such an overloaded condition.
Other minimal rotation latched shippers may use stunted threads that allow the wafer carrier to be rotated less than 30° to accomplish the latching. Such wafer carrier has the difficultly of requiring relatively precise angular positioning for initial placement of the top cover on the base before said rotation.
Other embodiments may use axially-projecting double thin walls. Such embodiments provide double sidewalls are connected at the ends of each segment. Thus, four separate wall portions are defined, all of which are distinct from one another and integral with the base. Due to the connecting portions, which connect each of the pairs of thin sidewall segments, a direct impact blow on the top cover will transmit the force of such blow directly from the top cover through said connecting portions to the wafers. This top cover also has features configured as nubs, which may engage a floppy disk.
Generally, all embodiments of the wafer carriers herein will be injection molded of thermoplastic material such as polypropylene. Such material requires structure such as ribs and channels for rigidity.
In that these shippers do not have the severe particulate control issues that are necessary for carriers in the fab processing environment, it is not necessary to have hermetic sealing. In fact, such hermetic sealing is inimical to robotic handling and easy manual handling, specifically the opening and closing of the shippers. Still, it is important to have the interface between the top cover and the base to provide the best sealing characteristics possible. Moreover, it is important to eliminate or reduce any bowing that occurs along one of the sidewalls intermediate the corners of the top cover or the base.
These types of containers may be utilized once and thrown away, or may be recycled and utilized multiple times. Although the product shipped in such containers can be of immense value, it is still important to reduce the manufacturing cost of the shippers to as great as extent as possible, consistent with the other necessary characteristics.
A most important characteristic of such wafer shippers for stackable wafers is that the shippers provide protection from damage due to shock during the transportation. This shock may consist of direct impact with the shipper's top cover or base, or consist of jarring of the entire shipper package. In either case, it is important to provide protection from damage to the wafers packed therein.
Moreover, it is important that such wafer shippers provide latching means of high integrity that do not inadvertently open during shipment or handling; for example, when a shipper is inadvertently dropped.
Such shippers are typically drop tested to determine the overall integrity of the shipper. Upon such dropping, unlatching, breakage of the shipper or damage to the wafers constitutes a failure. The impact during dropping, including drop testing, creates shear, compressive and torsional forces on the shipper components. The shipper, including the latches, must withstand combinations of these forces when loaded.
These shippers rely heavily upon the separation of materials between wafers or frames, which may be polyethylene sheet material with carbon providing a static dissipative characteristic, polyurethane foam, or other suitable, flexible thin sheet material. Typically, the packing material placed on the bottom and top of the stack will be the polyurethane foam that is compressible. The compressibility of the foam facilitates packing a variable number of wafers in a particular shipper, which can leave some undesirable discretion to the packer as to how many wafers and/or how much padding material is appropriate for a particular shipper. Moreover, inserting excessive, or even a full load, of wafers and foam padding can, in prior art wafer shippers, particularly those with latches on the diagonal corners, cause distortion and/or bowing of the top cover and/or base. This bowing may actually cause a gap between the top cover and base. Such a gap is visually undesirable, may provide a pathway to contamination of the contents, and may further affect the integrity of the container during impact or shock, causing breakage or unlatching.
If the shipper is underpacked with foam or other packing material, breakage may occur at limits under normal impact limits. Known prior art wafer carriers have provided no ready assistance in identifying an appropriate range of foam and wafer stacked thickness, which is optimal for providing security to the wafers. Similarly, the stacked wafer shippers with the latches on the diagonally opposite corners have provided no means to minimize the visibility of the gap at the sides of the shipper when the shipper is fully loaded or slightly overloaded. Moreover, these prior art shippers have inadequately provided structural means to the base and top cover to provide rigidity and minimize said bowing and gaps at the interface.